1. Field of the Invention
This invention relates to an adhesive composition containing a moisture absorbent, and more particularly to an adhesive composition containing a moisture absorbent that shows a pH property of acidity or alkalinity by absorption of moisture. The term “pH property” as used in this specification, claims, drawing and abstract of the disclosure means acidity, neutrality or alkalinity (basicity) shown by a material, which is the term to describe characteristics of pH (hydrogen ion concentration).
2. Description of the Related Art
A resin is applied to a joint for use in a vehicle such as an automobile so as to allow the joint to have a sealing function (such as watertightness and airtightness). A vinyl chloride resin sealing compound, an acrylic sol sealing compound or the like are used as the sealing compound. Among them, the vinyl chloride resin sealing compound is mainly used from the viewpoints of cost performance, ease in handling or the like.
On the other hand, a three-wet painting technique using a water-based intermediate coat and a water-based top coat that are baked simultaneously has been introduced in a painting or a coating process of a recent automobile production line from the viewpoints of shortening the process with consideration for environmental problems. Even the sealing compound needs to be adaptable to the three-wet painting technique. Moreover, a paint appearance should be similar to a conventional one even after such water paint is applied and then baked. A water resistant test was conducted after applying the water paint to the vinyl chloride resin sealing compound that was mainly used as the sealing compound and then baking. However, according to the test, it was proved that a great number of swellings were generated on a painted surface of the sealing compound, thereby having a problem that a quality in appearance is impaired.
In order to solve such problems in the vinyl chloride resin sealing compound, Japanese Patent Laid-Open Publication No. 7-082549 discloses a vinyl chloride plastisol sealing compound. In the invention described in the Japanese Laid-Open Publication, a polyester plasticizer having a molecular weight of 1500 or more is used as 25 to 60% by weight of a plasticizer which is included in the vinyl chloride plastisol sealing compound. It prevents the plasticizer from being readily extracted from the sealing compound and transferred to the intermediate coat. Moreover, such vinyl chloride plastisol sealing compound has an excellent paint performance so that a phenomenon such as stringiness or dripping off of the sealing liquid is not readily caused in the process of applying the sealing compound.
In the techniques described in the above Japanese Patent Laid-Open Publication No. 7-082549, an effect to improve paintability is obtained at an initial stage. However, the invention also has a problem as follows. That is, a phenomenon is unavoidable that a great number of swellings are generated on a painted surface of the sealing compound when a water resistant test is performed after painting and baking.
The present invention attempts to solve such problems. It is an object of the present invention is to provide an adhesive composition containing a moisture absorbent that shows acidity or basicity by absorption of moisture from a vinyl chloride resin sealing compound or the like, wherein no swelling is generated on a paint surface of the adhesive composition and a quality in paint appearance is maintained even if a water resistant test is performed after applying water paint and baking it.